Update handler.py

utf-8 for b64 strings

handler.py

@@ -672,7 +672,7 @@ class EndpointHandler():
                 output_image = output_image.convert('RGB')
                 output_image.save(buffered, format="png")
                 img_str = base64.b64encode(buffered.getvalue())
-                base64_strings.append(img_str)
+                base64_strings.append(img_str.decode('utf-8'))
 
             return base64_strings